Method for enhancing the performance of a video camera

Abstract

A method for enhancing the performance of a video camera capable of switching between night-mode and day-mode operation comprises: acquiring a first sequence of images with the video camera with an IR-transmission filter of known transmission characteristics in front of an image sensor of the video camera, the IR transmission filter having a transmission in the IR-region of above 30%, and acquiring a second sequence of images with the video camera without the IR-transmission filter. The method then uses the first and second image sequences to measure the contribution from visual light, or a contribution of IR radiation to images in the first or second stream of images. The measurements utilize an assessment of the calculated contribution to improve the performance of the video camera by switching the video camera from night-mode to day-mode, or add color information to images acquired with IR-radiation to the image sensor.

The invention claimed is: 
     
       1. A method for enhancing the performance of a video camera capable of switching between night-mode operation and day-mode operation, comprising:
 acquiring a first sequence of images with the video camera without a second filter setup arranged in front of an image sensor of the video camera and without any IR-cut filter arranged in front of the image sensor, i.e., with the video camera operating in night-mode, 
 acquiring a second sequence of images with the video camera with the second filter setup in front of the image sensor of the video camera, the second filter setup comprising an IR-transmission filter of known transmission characteristics and having a transmission in the IR-region of at least 30% and below 100% and spatially uniform transmission over its active area such that every pixel of the image sensor will be affected uniformly, wherein the second filter setup has a transmission of visual light of 100% and wherein the first and second sequences of images are consecutive or interleaved, 
 using the first and the second sequences of images to calculate a contribution of visual light in images in the first sequence of images and the second sequence of images, and 
 utilizing an assessment of the calculated contribution to improve the performance of the video camera by, switching the video camera from night-mode to day-mode based on the contribution of visual light in the images in the first sequence of images and the second sequence of images, or to deduce and add color information to images acquired with full or partial transmission of IR-radiation to the image sensor based on the contribution of visual light in the images in the first sequence of images and the second sequence of images. 
 
     
     
       2. The method of  claim 1 , wherein the assessment is used to add color information to portions of the image otherwise having a skewed color information due to IR-contribution. 
     
     
       3. The method of  claim 2 , further comprising segmentation of an image into areas with motion and areas without motion, wherein the addition of color information is applied in areas without motion. 
     
     
       4. The method of  claim 1 , wherein the acquisition of the first and second sequence of images is performed at regular intervals or as a result of an event, such that color information is updated at a lower rate than a current frame rate of the video camera. 
     
     
       5. The method of  claim 1 , wherein the assessment is performed at a resolution of groups of pixels, wherein the image is divided into multiple groups of pixels. 
     
     
       6. The method of  claim 1 , wherein different regions of the image have different weights in the assessment of the calculated contribution. 
     
     
       7. The method of  claim 1 , wherein the IR-transmission filter has a transmission in the IR-region of above 40%, 50%, 60%, 70%, 80%, or 90%. 
     
     
       8. A video camera capable of switching between night-mode operation and day-mode operation, comprising:
 an image sensor acquiring a first sequence of images without a filter setup arranged in front of an image sensor and without any IR-cut filter arranged in front of the image sensor, i.e., with the video camera operating in night-mode, 
 the image sensor acquiring a second sequence of images with the filter arranged in front of the image sensor, the filter setup comprising an IR-transmission filter of known transmission characteristics and having a transmission in the IR-region of at least 30% and below 100% and spatially uniform transmission over its active area such that every pixel of the image sensor will be affected uniformly, wherein the second filter setup has a transmission of visual light of 100% and wherein the first and second sequences of images are consecutive or interleaved, 
 an actuation mechanism for transferring the filter setup to and from a position in front of the image sensor, 
 a processor for receiving the first and the second sequences of images to calculate a contribution of visual light in images in the first sequence of images and the second sequence of images, and utilizing an assessment of the calculated contribution to improve the performance of the video camera by, switching the video camera from night-mode to day-mode based on the contribution of visual light in the images in the first sequence of images and the second sequence of images, or to deduce and add color information to images acquired with full or partial transmission of IR-radiation to the image sensor based on the contribution of visual light in the images in the first sequence of images and the second sequence of images. 
 
     
     
       9. The video camera of  claim 8  wherein the IR-transmission filter has a transmission in the IR-region of above 40%, 50%, 60%, 70%, 80%, or 90%.